Microfluidic channels and the control of fluid and/or fluid suspended particle flow within them are useful in many applications. Drug discovery and diagnosis of disease, for example may require the control of movement of reagents and biological samples to and from chambers where reactions may take place. Sorting of cells for example may require cells arriving from one or more sources to be sent to one or more destinations. Such sorting may require a high speed valves to redirect the flow of fluid and particles dynamically based on analysis of the type of cells or particles arriving, on a cell by cell or particle by particle basis.
One method to affect fluid flow within a channel is to create a vapor bubble within the channel, or adjacent to the channel so as to affect the flow within the channel. Small 10-100 μm vapor bubbles can be created within 1-100 μS of turning on a laser and they will also re-condense into liquid in approximately the same time frame when the laser is turned off.
It was disclosed by Jian et al., LASER-ACTUATED MICRO-VALVES AND MICRO-PUMPS, 16th International Solid-State Sensors, Actuators and Microsystems Conference, Jun. 5-9, 2011, that vapor bubbles have been created by the heating effect of a laser light being absorbed by a gold target on the channel wall. U.S. Pub. No. 2011/0030808, disclosed that vapor bubbles have been created in cavities adjacent to a channel with electrometric walls so as to deflect the walls and create changes in the fluid flow within the channel. U.S. Pub. No. 2008/0261295 disclosed that lasers are used to trap particles by surrounding them with light, but not through vapor bubble creation.
The prior art, e.g., U.S. Pub. No. 2011/0030808, has several shortcomings; first in an application where cells or particles within the fluid are sorted into one of two paths for example, even though particles may be selectively deflected to enter one or the other channel, fluid flow is present in both paths at all times, thus the sample fluid containing the particles of interest is continuously diluted. This type of dilution is not present in “Sort in air” systems (e.g., U.S. Pat. No. 6,281,018 and U.S. Pat. No. 5,700,692), where only the sample of interest is sent into the collection chamber. A further shortcoming of U.S. Pub. No. 2011/0030808 is that it requires the construction of flexible flow channels of an electrometric substance, where as a glass or quartz cuvette would be more durable.
The prior art (e.g., Jian et al.) also has shortcomings in that it requires an opaque target to be deposited on one side of the flow channel walls, further because heat is absorbed by the walls and then transferred to the fluid, the action is very slow in the several millisecond regime.